.tabbar_homepage li.current a b {
To explain what this is doing we have the first bit
.tabbar_homepage which means that what we're going to be working with is anything with that class applied. Second is
li which tells it any list-item element which that class applied, thirdly we have .current which applies ONLY to list-items within the tabbar_homepage class ie.,
<div class="tabbar_homepage">
<ul><li class="current">blah</li></ul>
</div>
Next, we have
a which will look for an anchor (a) TAG, ie.,
<a href="hello.html">Hello</a>. Now keep in mind that that was looking for a TAG, so when we get to the
b bit it is looking for a b TAG ie.,
<a href="hi.html"><b>Hello</b></a> So to match that style you would need this:
<!-- I'm using div as a container, doesn't matter what you use -->
<div class="tabbar_homepage">
<ul>
<li class="current"><b><a href="test.html">Test</b></a></li>
</ul>
</div>
So, after all that, we realize that there is no class
ab which is what you were looking for, since it is looking for the b tag inside the a tag.